Uniformly 15N-Labeled Recombinant Ricin A-chain as an Internal Retention Time Standard for Increased Confidence in Forensic Identification of Ricin by Untargeted Nanoflow Liquid Chromatography-Tandem Mass Spectrometry

Journal Article · Tue Nov 05 04:00:00 EST 2019 · Analytical Chemistry

DOI:https://doi.org/10.1021/acs.analchem.9b03389· OSTI ID:1574473

Merkley, Eric D. ^[1]; Burnum-Johnson, Kristin E. ^[1]; Anderson, Lindsey N. ^[1]; Jenson, Sarah C. ^[1]; Wahl, Karen L. ^[1]

---

1. BATTELLE (PACIFIC NW LAB)

Ricin, a toxic protein from the castor plant, is of forensic and biosecurity interest because of its high toxicity and common occurrence in crimes and attempted crimes. Qualitative methods to detect ricin are therefore needed. Untargeted liquid chromatography-tandem mass spectrometry (LC-MS/MS) proteomics methods are well-suited because of their high speci-ficity. Specificity in LC-MS/MS comes from both the LC and MS components. However, modern untargeted proteomics methods often use nanoflow LC, which has less reproducible retention times than standard-flow LC, making it challenging to use retention time as a point of identification in a forensic assay. We address this challenge by using retention times rela-tive to a standard, namely uniformly 15N–labeled ricin A-chain produced recombinantly in a bacterial expression system. This material, added as an internal standard prior to trypsin digestion, produces a stable isotope labeled standard for every ricin tryptic peptide in the sample. We show that the MS signals for 15N and natural isotopic abundance ricin peptides are distinct, with mass shifts that correspond to the numbers of nitrogen atoms in each peptide or fragment. We also show that, as expected, labeled and unlabeled peptides coelute, with relative retention time differences of less than 0.2%.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1574473
• Report Number(s): PNNL-SA-145704
• Journal Information: Analytical Chemistry, Journal Name: Analytical Chemistry Journal Issue: 21 Vol. 91
• Country of Publication: United States
• Language: English

Related Subjects

ricin
mass spectrometry
isotope
nitrogen-15
retention time
proteomics
forensics